Assembly of mitochondrial ribosomes requires the transport of ribosomal proteins from their site of synthesis in the cytoplasm into mitochondria and the synthesis of ribosomal RNA's on m-DNA as a precursor molecule which is cleaved and methylated. It is proposed to study the control of this assembly process making use of a mutant Neurospora strain (Mi-l-poky) which shows a defect in assembly of small m-ribosomal subunits. The defect is apparently linked to mitochondrial-DNA. The experiments will involve a study of the control of enzymatic methylations within mitochondria, a search for nascent and maturing ribosomal subunits, and an investigation of how post-transcriptional modification of proteins may affect their transport into and function within mitochondria. BIBLIOGRAPHIC REFERENCES: Lambowitz, Alan and D.J.L. Luck. Methylation of mitochondrial RNA species in the wild type and poky strains of Neurospora crassa. J. Mol. Biol. (1975), 96:207-214.